The present invention relates to a vacuum brake power booster for automotive vehicles of the type having a vacuum casing which is sealingly subdivided by an axially movable wall into a vacuum chamber and a working chamber, and a mechanically actuatable control valve connecting the working chamber to the vacuum chamber and/or to the atmosphere. The axially movable control valve casing is made of thermoplastics and accommodates in an axial bore an elastomeric reaction plate which abuts on a head flange of a push rod for transmitting the brake force onto an actuating piston of a master cylinder that is mounted to the vacuum casing on its vacuum side. The movable wall is coupled to the control valve casing and a guide sleeve serves to axially guide the push rod. The sleeve includes a radial flange. The invention further relates to a method for manufacturing such a vacuum brake power booster.
A vacuum brake power booster of this type is disclosed in applicant's German application No. P 33 44 110.3. In that brake power booster, a pressure plate is arranged between the reaction plate and the push rod. and a guide plate is incorporated in a recess of the control valve casing or in a clamping sleeve connected to the control valve casing. The guide plate has a central bore and its radially internal rim is shaped to form a neck or collar which extends axially in the direction of the master cylinder and serves to hold and guide the push rod, whose end or head portion close to the control casing cooperates with the pressure plate.
A shortcoming in this brake power booster is the way the guide plate is fastened to and/or axially secured at the control valve casing. In particular there must be a metal part in which indentations are provided to retain the guide plate on an end surface of the control valve casing. The part is formed by an axial neck of a diaphragm plate which, together with a rolling diaphragm, is fastened to the control valve casing. This arrangement does not form a particularly good weight-saving design for a vacuum brake power booster in which diaphragm plates of aluminum are used. In view of cracks that can occur during deep-drawing of the aluminum, a separate part made of a metal of better deep-drawing quality must be used. The consequence thereof is a two-part design of the diaphragm plate entailing higher costs. Another shortcoming is found in the mounting of the guide plate which can be done in the axial and in the radial directions. Also shaping of the control valve casing and the channels therein is restricted.